This invention relates to circuits for compensating the output of a measuring transducer with the output from a compensating transducer such as a circuit for compensating the output of a pressure transducer with the output of a temperature transducer.
The application of modern day instrumentation and technology often requires the precise measurement of environmental conditions, such as temperature and pressure. The transducers that are used to sense the environmental conditions are often dual type transducers. That is to say, a transducer whose primary application is that of a pressure transducer is sensitive to variations in temperature, and similarly, a temperature transducer is sensitive to variations of pressure. In either case, this sensitivity is considered an anomaly of the primary application and is undesirable. In applications where the precise measurements of environmental conditions are required, the dual sensing of the transducers are unwanted, particularly in applications such as oil well instrumentation where precision instruments are inserted into the extreme environmental conditions present in the oil well or "down hole". The common type of pressure transducer used for this application is the bourdon tube transducer which provides the measurement of pressure and in some cases temperature. Variations in temperature will cause a change in the modulus of elasticity of the bourdon tube material of the pressure transducer, and as such, will result in an error in the output of the transducers.
One method of dealing with this problem was disclosed in U.S. Pat. No. 4,033,186 which provided a method and apparatus for down hole pressure and temperature measurements and also disclosed a multiplexer for processing the down hole gage signals from a plurality of parametric sensors and a digital converter for digitizing the output of the multiplexer.
In U.S. Pat. No. 3,977,245 there was disclosed an apparatus for digitally recording the values of pressure and temperature and other parameters in a bore hole logging instrument. In one embodiment, the values of the earth parameters are converted to an AC signal whose frequency is a function of the value of the measured earth parameter. Clock means are provided for presenting at selected time intervals voltage pulses of selected short time length. The clock signal is gated to a counter for a selected short interval of time, and the count of the counter becomes a measure of the earth parameter. A solid state memory is provided in the output of the counter for the storing of the measured earth parameters in the form of binary bits stored in the memory.